For the Firefox 3 and blogger.com post I wanted to include a screen grab of the settings I was using. I discovered that this is very easy on OS X I used the site below to quickly find the keyboard shortcuts.
⌘ ⇧ 3 Screen to png file on desktop
⌘ ⇧ 4 + Drag: Selection to png file on desktop
⌘ ⇧ 4 + Spacebar: Window (click camera) to png file
It is possible to change the output format by typing the following at the terminal
$defaults write com.apple.screencapture type jpg